Rare Polio-Like Syndrome Cases on the Rise in US

Megan Brooks

October 05, 2016

Confirmed cases of acute flaccid myelitis (AFM) in the United States have increased in 2016 compared with 2015, and the cause remains unclear, federal health officials say.

AFM is a rare polio-like syndrome that affects the nervous system, specifically the spinal cord. It can result from a variety of causes, including viral infections. AFM is characterized by rapid onset of weakness in 1 or more limbs and distinct abnormalities of the spinal cord gray matter on MRI.

From January 1 to August 31, 2016, 50 people in 24 states across the country were confirmed to have AFM, up from 21 people in 16 states in 2015, officials with the Centers for Disease Control and Prevention (CDC) say.

The CDC started actively investigating AFM in August 2014, when it noticed an increase in reports of people across the United States with AFM for which no cause could be found.

From August to December 2014, 120 people in 34 states were confirmed to have AFM. Most patients were aged 21 years and younger.

"We continue to receive reports of sporadic cases of AFM," the CDC says.

The agency cautions that interpreting trends in AFM is difficult because reporting started only in 2014 and is voluntary in most states. Also, because AFM reporting is relatively new, there may initially be more variability in the data from year to year, it points out. This makes it tough to interpret or compare case counts between years. One possible reason for the differences in annual reporting is more awareness among and reporting by healthcare providers and health departments, the CDC says.

For the confirmed AFM cases reported since August 2014, the patients' symptoms have been similar to those caused by certain viruses, including poliovirus, nonpolio enteroviruses, adenoviruses, and West Nile virus, the CDC says.

"Enteroviruses can cause neurologic illness, including meningitis. However, more severe disease, such as encephalitis and AFM, is not common. Rather, they most commonly cause mild illness," the CDC points out.

The CDC has tested patients with AFM for a wide range of pathogens that can cause AFM, but thus far it has failed to consistently detect a pathogen in the patients' spinal fluid.

The increase in AFM cases in 2014 coincided with a national outbreak of severe respiratory illness caused by enterovirus D68 (EV-D68). But the CDC says it did not consistently detect EV-D68 in the specimens collected from patients with AFM. In 2015, no cases of EV-D68 were detected, and so far in 2016, only limited sporadic cases of EV-D68 have been found in the United States.

Despite extensive testing, the CDC says it doesn't yet know the cause of the AFM cases, nor has it determined who may be at higher risk for AFM.

The CDC is actively investigating the AFM cases and monitoring disease activity. It is working closely with healthcare providers and state and local health departments to increase awareness and reporting for AFM and to investigate the AFM cases, risk factors, and possible causes of this illness.

The CDC encourages healthcare providers to "be vigilant for AFM among their patients, and to report suspected cases to their health departments."

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